Talk Five:

Digestion and Nutrition

Chapter 11

Human Biology (BIOL 104)

So, what do we usually eat?

Carbohydrates Protein Lipids

• Carbohydrates: To give us ENERGY! We need energy for heat, movement, and chemical reactions in our bodies.

• Proteins: Essential amino acid’s. Our body can’t make them; they must come from foods we eat.• Meat, milk, and eggs contain all the essential amino acids

we need

• Fats: Energy! We can use it or store it. Fat contains more energy than carbohydrates. 1 gram of Fat = 2x the energy in 1 gram of Carbs.• Used for Cell Membranes and Heat Insulation

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So, how do we digest food?• In the human digestive system, the process of digestion has many

stages, the first of which starts in the mouth (oral cavity).

• Digestion involves the breakdown of food into smaller and smaller components which can be absorbed and assimilated into the body.

• The secretion of saliva helps to produce a bolus which can be swallowed in the esophagus to pass down into the stomach.

• This initially results in the production of chyme which when fully broken down in the small intestine is absorbed into the blood.

• Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood, in the colon of the large intestine.

• The waste products of digestion are defecated from the anus via the rectum.

Digestion occurs in 5 stages

• 1: Mechanical processing and motility– Teeth, the tongue, and

various muscle layers start the process and send food on its journey

• 2: Secretion– Release of enzymes &

chemicals for digestion and absorption

• 3: Digestion– Chemical breakdown of food –

small molecules absorbed

• 4: Absorption– Nutrients move into the

blood

• 5: Elimination– Undigested and unabsorbed

residues excreted

The first step- Chewing and swallowing

• Types– Mechanical (physical)

• Chew• Tear• Grind• Mash• Mix

– Chemical• Enzymatic reactions to

improve digestion of –Carbohydrate

s–Proteins– Lipids

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The first step- Chewing and swallowing• Teeth mechanically break down food into

small pieces.

• Tongue mixes food with saliva

• Saliva contains amylase– helps break down starch.

• Mucus – protects soft lining of digestive system– lubricates food for easier swallowing

• Buffers• neutralizes acid to prevent tooth

decay

• Anti-bacterial chemicals – kill bacteria that enter mouth with food

• Epiglottis is a flap-like structure at the back of the throat that closes over the trachea preventing food from entering it.

From the wikimedia free licensed media file repository

From the wikimedia free licensed media file repository

Digestive Glands

• Groups of specialized secretory cells.

• Found in the lining of the alimentary canal or accessory organs.

Taste Buds• As the food particles

dissolve in the saliva they penetrate the cells of the taste buds located on the tongue and cheeks.

• Humans can differentiate between

• sweet • sour • salty • bitter

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The Esophagus• Approximately 10” long

• Functions include:– Secrete mucus– Moves food from the throat to

the stomach using muscle movement called peristalsis

• A good way to describe peristalsis is an ocean wave moving through the muscle.

– Has no role in chemical digestion – all it does is bring food (BOLUS) to stomach.

• Sphincters – ring of muscle that encircle tubes.– Contraction closes tubes– Keeps acid in stomach –

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The Stomach- Digestion and Storage

• The stomach acts as a temporary storage site for food.

• Food usually spends about 4 hours in the stomach.

• It has ridges which allow it to expand to store about 1.5 litres of food.

• The stomach is also the site of initial protein digestion.

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The Stomach- Digestion and Storage

• Millions of cells lining the stomach secrete various fluids known collectively as gastric fluids.

• Gastric fluid consists of mucus, hydrochloric acid, pepsinogens and other substances.

• Mucus coats and protects the lining of the stomach.

• Hydrochloric acid kills any harmful substances that have been ingested and it also converts pepsinogen into pepsin.

• Pepsin is a protein digesting enzyme that breaks large protein chains into smaller chains.

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The Stomach- Digestion and Storage

• Movement of food into and out of the stomach is controlled by circular muscles known as sphincters.

• One at the top of the stomach allows food from the esophagus to enter and prevents food from going back up into the esophagus.

• Another located at the bottom slowly releases partially digested food into the small intestine.

• Alcohol and some water are absorbed here – food is not.

• The partially digested food is called chyme.

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The Intestines• The intestines are

named for their diameter, not length.

• The small intestine is up to 7 m in length but only 2.5 cm in diameter.

• The large intestine (also known as the Colon) is only 1.5 m in length but 7.6 cm in diameter.

The small intestine• Where much of the digestion

and absorption of food takes place.

• It receives bile juice and pancreatic juice through the hepato-pancreatic duct, controlled by a sphincter

• The small intestine is where most chemical digestion takes place.

• Most of the digestive enzymes that act in the small intestine are secreted by the pancreas and enter the small intestine via the pancreatic duct

The small intestine

• Approx 20 feet in length– First 25 cm – Duodenum

• A duct brings Bile (from Liver and Gallbladder)– emulsifies fat – disperses in water

• A duct brings Pancreatic Juice from Pancreas. Contains – NaCHO3 – neutralizes chyme

– enzymes to complete food digestion.

• The small intestine contains Villi –

absorb nutrients.

• Sugars & amino acids enter blood capillaries

• Glycerol and fatty acids enter lymph nodules

• Almost 90% of our daily fluid intake is absorbed in the small intestine.

Small Intestine• Nutrients from the food pass

into the bloodstream through the small intestine walls.

• Absorbs:– 80% ingested water– Vitamins– Minerals– Carbohydrates– Proteins– Lipids

• Secretes digestive enzymes

Segmentation in the Small Intestine

• Unlike peristalsis, which predominates in the esophagus, segmentation contractions occur in the large intestine and small intestine, while predominating in the latter

• When the contractions of the intestinal wall move chyme in both directions to allow mixing with the secretions of the intestines.

The small intestine - Villi• Increases surface area of

small intestine

• Each villus contains a capillary network along with a lacteal.

• The lacteal is a vessel of the lymphatic system.

• End products of protein and carbohydrate digestion enter the capillary network.

• End products of fat digestion are absorbed into the lacteal.

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The small intestine - Villi• The Hepatic Portal Vein takes all absorbed nutrients

(except large fat molecules) from villi to the liver for further processing and storage.

The large Intestine• 4-1/2 feet long

– Absorbs water, salts and some vitamins

• Stores indigestible material for defecation

• Contains the: – Cecum (blind end of

ascending colon).– Appendix located here.

• Colon- Ascending, Transverse, Descending and Sigmoid.

• The sigmoid Colon enters Rectum (last 20 cm of large intestine, where it opens at the Anus.

• Feces: ¾ water and ¼ solidCopyright ©The McGraw-Hill

Companies; used with permission

The large Intestine• Functions• Bacterial digestion• Ferment carbohydrates• Protein breakdown

• Absorbs more water• Concentrate wastes

• Solid materials pass through the large intestine.

• These are undigestible solids (fibers).

• Water is absorbed.• Vitamins K and B are reabsorbed

with the water.• Rectum- solid wastes exit the

body.Copyright ©The McGraw-Hill

Companies; used with permission

The large Intestine – You’ve got company!

• Living in the large intestine is a community of helpful bacteria– Escherichia coli (E. coli)• produce vitamins

– vitamin K; B vitamins

• generate gases– by-product of bacterial

metabolism – methane, hydrogen sulfide

The Accessory Organs • The Liver:

• 100,000 lobules monitor and clean blood, produce bile for gallbladder.

• Detoxify blood, store iron, vitamins A, D, E and K.

• Helps regulate blood sugar (glycogen, glycerol, Amino acids), destroys old blood cells.

• Helps regulate cholesterol (bile salts).

• Makes urea which is worked on by kidneys

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The Accessory Organs • The Gall Bladder:

• Pouch structure located near the liver which concentrates and stores bile

• Bile duct – a long tube that carries BILE.

• The top half of the common bile duct is associated with the liver.

• The bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.

• Bile emulsifies lipids (physically breaks apart FATS) Copyright ©The McGraw-Hill

Companies; used with permission

The Accessory Organs • The pancreas:

• An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine)

• Pancreatic juice digests all major nutrient types.

• Exocrine pancreas produces NaHCO3, amylase (starch), trypsin (protein) and lipase (fat).

• Endocrine pancreas produces insulin and glucagon.

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Human Nutrition• The provision to obtain the

essential nutrients necessary to support life and health.

• In general, people can survive for two to eight weeks without food, depending on stored body fat and muscle mass.

• Poor nutrition is a chronic problem linked to poverty, poor nutrition understanding and practices, and deficient sanitation and food security.

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Human Nutrition• Malnutrition globally provides

many challenges to individuals and societies.

• Lack of proper nutrition contributes to worse class performance, lower test scores, and eventually less successful students and a less productive and competitive economy.

• Malnutrition and its consequences are immense contributors to deaths and disabilities worldwide.

• Promoting good nutrition helps children grow, promotes human development and advances economic growth and eradication of poverty.

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So, what do we usually eat?

Carbohydrates Protein Lipids

• Carbohydrates: To give us ENERGY! We need energy for heat, movement, and chemical reactions in our bodies.

• Proteins: Essential amino acid’s. Our body can’t make them; they must come from foods we eat.• Meat, milk, and eggs contain all the essential amino acids

we need

• Fats: Energy! We can use it or store it. Fat contains more energy than carbohydrates. 1 gram of Fat = 2x the energy in 1 gram of Carbs.• Used for Cell Membranes and Heat Insulation

Copyright ©The McGraw-Hill Companies; used with permission

Eating a balanced diet

• What happens if a human’s diet is missing an essential nutrient?– deficiency diseases• scurvy — vitamin C (collagen production)• rickets — vitamin D (calcium absorption)• blindness — vitamin A (retinol production)• anemia — vitamin B12 (energy production)

• Need to make sure you get enough protein

• 20 amino acids to make protein– 12 amino acids humans can produce – 8 we have to eat = “essential amino

acids”

• Grains (like corn) have 6 amino acids (orange box)– missing 2

• Beans (like soybean & red beans) have 6 amino acids (green box)– missing different 2

• mix beans & grains for complete group of amino acids– rice & beans– taco/tortilla & beans– tofu & rice– peanut butter & bread

Vegetarian diets

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Vitamins

• Organic compounds needed by the body in small, but essential amounts

• Cannot be synthesized by the body in sufficient amounts

• Function in a variety of ways in metabolic reactions

• Thirteen known vitamins

• Water-Soluble Vitamins Versus Fat-soluble Vitamins

Water-Soluble Vitamins

Pantothenic acidBiotinB12

(cyanocobalamin)

Folic acid B6 (pyridoxine)

C (ascorbic acid)

B1 (thiamin)

B2 (riboflavin)

Niacin

Fat-soluble Vitamins

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Vitamins• Vit A- Antioxidant: healthy eyes, hair, bones• Vit D – Steroid: bones and teeth• Vit E – Antioxidant: healthy unsaturated fats• Vit K – Clotting blood• Vit C – Antioxidant: Capillaries, bones teeth• Vit B1 – coenzyme for cellular respiration• Vit B6 – coenzyme for hormones and hemoglobin• Vit B12 – coenzyme for synthesis of nucleic acid• Biotin – coenzyme for metabolism of ammino acids

and fatty acids

Minerals

• Essential inorganic elements

• Involved in a variety of metabolic processes

• Major minerals versus trace minerals

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Essential dietary minerals• Chlorine: as chloride ions along with Sodium

• Magnesium: required for processing ATP and related reactions – builds bone, causes strong peristalsis, increases flexibility, increases

alkalinity.

• Phosphorus: required component of bones; essential for energy processing Approximately 80% is found in inorganic portion of bones and teeth. Phosphorus is a component of every cell, as well as important metabolites, including DNA, RNA, ATP, and phospholipids. – Also important in pH regulation. Food sources include cheese, egg

yolk, milk, meat, fish, poultry, whole-grain cereals, and many others.

• Potassium: a very common electrolyte (heart and nerve health). With sodium, potassium is involved in maintaining normal water balance, osmotic equilibrium, and acid-base balance. – In addition to calcium, it is important in the regulation of

neuromuscular activity. Food sources include bananas, avocados, vegetables, potatoes, legumes, and mushrooms.

Trace minerals• Cobalt required for biosynthesis of vitamin B12 family of coenzymes

• Copper required component of many redox enzymes, including cytochrome c oxidase

• Chromium required for sugar metabolism

• Iodine required for important organs as breast, stomach, salivary glands, thymus etc.

• Iron required for many enzymes, and for hemoglobin and some other proteins

• Manganese required for the processing of oxygen

• Nickel present in urease

• Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase

The End!